BACKGROUND: Garden sage (Salvia officinalis L., Lamiaceae) has gained importance during the last decade as a natural antioxidant, mainly owing to the antioxidant secondary plant metabolites rosmarinic acid (RA) and diterpenes such as carnosic acid. The aim of this work was to study the biomass production, the concentrations of total phenolics and RA and the essential oil of garden sage in response to phosphorus (P) supply. The treatments included P fertilisation and inoculation with arbuscular mycorrhizal fungi (AMF), since AMF are the most efficient biotic factor promoting the P uptake of plants.